1. Field of the Invention
The present invention relates to a recording disk apparatus, which is represented by a magnetic disk apparatus such as a hard disk drive unit (HDD), and in particular, to a housing thereof.
2. Description of the Prior Art
It is well known that a magnetic disk apparatus makes noise in the seek operation because of the rotation of the magnetic disk. The noise is originally caused by vibration which is generated by the rotation of the magnetic disk and transmitted to the housing through the rotation axis and the like. Accordingly, an overall housing with high rigidity, formed by die-casting, serves to suppress the noise. On the other hand, it is preferable to employ a press for forming a housing when taking account of reduction in weight and manufacturing cost. In particular, reduction in manufacturing cost for housings becomes one of the indispensable factors in distributing cheap personal computers in the market.
Currently, most housings comprise a box-shaped housing body formed by die-casting and a cover plate closing the opening of the housing body. This structure enables a cover to be formed with a press. However, a cover with low rigidity tends to vibrate, so that the generation of noise cannot be avoided. It is known to suppress noise by employing a cover made of a vibration suppression metallic plate, which in general comprises a pair of metallic plates sandwiching a synthetic resin layer. The plate may absorb vibration so that the suppression of noise can be achieved.
A housing accommodates many components such as a magnetic disk for recording, a magnetic head for reading and writing information out of and into the magnetic disk, an actuator for driving a carriage supporting at the tip end the magnetic head, a spindle motor for driving the magnetic disk for rotation, and the like. Employment of a box-shaped housing tends to lead to trouble in assembling components, because the side walls of the housing hinder the assembling operation. It is known to overcome this inconvenience by employing a housing comprising a base plate and a cover formed by deep-drawing. This structure allows operators to easily assemble components on the base plate, thereby improving the efficiency in assembling operation.
On the other hand, a cover formed by deep-drawing cannot suppress vibration. Accordingly, a vibration suppression metallic plate is adhered to the outer surface of the cover around a screw which connects the rotation axis of the magnetic disk to the cover, as is disclosed in Japanese Patent Laid-open No. 9-128955, for example.
Recently, some factors, such as improved performance of spindle motors, appropriate management on electric current to spindle motors, and the like, have served to suppress vibration caused by the rotation of a magnetic disk. As a result, vibration generated by driving operation of an actuator comes to occupy large percentage in the cause of the total noise. The vibration from an actuator is transmitted to the cover through the rotation axis of the carriage, thereby making noise.
The employment of the above-described box-shaped housing serves to suppress vibration from an actuator because the overall cover is made from a vibration suppression metallic plate. Still, the increase in thickness of the cover leads to a reduction in the interior space of the overall housing. The technique disclosed in the above mentioned publication completely fails to consider vibration caused by an actuator.